Change string to date and joining on date range in Oracle SQL - sql

Question

I have below two tables:
~ What I am looking to do: I want to append the Price from Table 2 (t2) to Table 1 (t1), by joining on Quantity and YYYY_MM. Each t2.price was active in a certain time range (t2.Price_Active_Date_From and t2.Price_Active_Date_To), and the t1.Order_YYYYMM should fall within this range. Year 9999 indicates that the price has no end date yet, and is therefore still active. I also want to find which price was active 1 year prior to the order date
So the result should look like:
What I have tried below so far, which works to get the Price_Active_At_Order, but I am not sure how to get Price_Active_PY when my date values are strings:
select distinct
t1.Product_NR,
t1.Customer,
t1.Quantity,
t2.Price as Price_Active_At_Order,
t1.Order_YYYYMM as Order_Date
from Table_1 t1
join Table_2 t2 on t1.Product_NR = t2.Product_NR
and t1.Quantity = t2.Quantity
and t1.Order_YYYYMM between t2.Price_Active_Date_From and t2.Price_Active_Date_To

Answer 1

Two things to point out:
Line 6 : te.Order_YYYYMM as Order_Date change to t1.Order_YYYYMM as Order_Date
Line 13,14,15 : where clause is incomplete and unnecessary, remove it
Your code should work fine with the changes above.
select distinct
t1.Product_NR,
t1.Customer,
t1.Quantity,
t2.Price as Price_Active_At_Order,
t1.Order_YYYYMM as Order_Date
from Table_1 t1
join Table_2 t2 on t1.Product_NR = t2.Product_NR
and t1.Quantity = t2.Quantity
and t1.Order_YYYYMM between t2.Price_Active_Date_From and t2.Price_Active_Date_To

Answer 2

If you want to find a single row in table2 that can supply the complete quantity corresponding to a table1 row at the minimum price then, from Oracle 12, you can use a LATERAL join:
SELECT *
FROM table1 t1
LEFT OUTER JOIN LATERAL (
SELECT price,
price_active_date_from,
price_active_date_to
FROM table2 t2
WHERE t1.product_nr = t2.product_nr
AND t1.quantity <= t2.quantity
AND t1.order_yyyymm BETWEEN t2.price_active_date_from
AND t2.price_active_date_to
ORDER BY t2.price ASC
FETCH FIRST ROW ONLY
) t2
ON (1 = 1)
Which, for the sample data:
CREATE TABLE table1 (product_nr, customer, quantity, order_yyyymm) AS
SELECT 10023, 'X', 20, 202104 FROM DUAL UNION ALL
SELECT 10023, 'Y', 10, 202203 FROM DUAL UNION ALL
SELECT 10334, 'X', 1, 202204 FROM DUAL;
CREATE TABLE table2 (product_nr, quantity, price, price_active_date_from, price_active_date_to) AS
SELECT 10023, 1, 100, 202101, 999912 FROM DUAL UNION ALL
SELECT 10023, 10, 80, 201605, 202012 FROM DUAL UNION ALL
SELECT 10023, 10, 120, 202101, 202205 FROM DUAL UNION ALL
SELECT 10023, 20, 250, 202101, 999912 FROM DUAL UNION ALL
SELECT 10023, 100, 400, 202101, 202111 FROM DUAL UNION ALL
SELECT 10334, 1, 25, 202101, 202111 FROM DUAL UNION ALL
SELECT 10334, 1, 30, 202112, 202205 FROM DUAL;
Outputs:
PRODUCT_NR
CUSTOMER
QUANTITY
ORDER_YYYYMM
PRICE
PRICE_ACTIVE_DATE_FROM
PRICE_ACTIVE_DATE_TO
10023
X
20
202104
250
202101
999912
10023
Y
10
202203
120
202101
202205
10334
X
1
202204
30
202112
202205
If you want to find the row in table2 that can supply the quantity from the cumulative quantities between that row and the preceding rows within the date range ordered by ascending price then you can use:
SELECT *
FROM table1 t1
LEFT OUTER JOIN LATERAL (
SELECT price,
price_active_date_from,
price_active_date_to
FROM (
SELECT price,
price_active_date_from,
price_active_date_to,
SUM(quantity) OVER (ORDER BY price ASC) AS quantity
FROM table2 t2
WHERE t1.product_nr = t2.product_nr
AND t1.order_yyyymm BETWEEN t2.price_active_date_from
AND t2.price_active_date_to
) t2
WHERE t1.quantity <= t2.quantity
ORDER BY t2.price ASC
FETCH FIRST ROW ONLY
) t2
ON (1 = 1)
Which, for the sample data, has the same output.
db<>fiddle here